I have a weber performer kettle grill in which i use lump charcoal. Should I sear my meats and poultry with the lid on or off. I realize to use te lid when cooking longer cuts of meats, but i like my steks rare and tend to overcook them with the lid on

I always keep the lid off when searing my steaks- usually NY strips. You want that grill as hot as can be, and keeping the lid off is the way to do this. Once seared, than I push to the side of the grill (i.e. to a cooler spot) and cover until done, which for me is medium rare to mediumish- just a little bit of pink for me. Hope this helps.

Sounds like, for the most part, you wouldn't need to close the lid. You're searing them on the outside and keeping it rare on the inside. Closing the lid promotes cooking the inside of the meat through more efficiently, which is not your goal. So unless you have a thick cut of meat, say 1-1/2" or more, you would keep the lid open.

Chicken, however, should never be served rare. So I would recommend a medium heat and you could close the lid to cook the meat completely through. I don't always close the lid because I like to keep an eye on them so they don't over cook.

Weber promotes two practices that I disagree with. First is always cover the grill. I never cover for steaks up to about 2", chicken parts, sausages and similar stuff. I close the lid for roasts, whole chickenas and indirectly cooked stuff.

The other thing they say that I don't do is "oil the food, not the grill." I wipe my grates with an oiled paper towel. This one may be their attempt to avoid being sued by some moron spraying oil on a lit grill.

On the show Steven has said that a general rule of thumb is to grill with the lid on if the cut of meat is thicker than you hand and vise versa. I have used this method and it works pretty well. With grilling and bbq'n there is no exact way to do things, its all personal perference, and thats the beauty of it.

Grilling hot and uncovered helps to get that nice seared crust on the outside while keeping your meat nice and pink inside. It also helps to start with a cool dry steak. Oil and lipids are great, but if there is water or water based marinade in the meat, this can steam the inside and take some of that pinkness away if you like rare meat. The fat will make your steak juicy anyway.
When the lid is closed your using a combination of grilling and baking which cooks the inside more too. That's not a bad idea if you like your meat med well or well done and you want your meat cooked all the way through. That's definitely not a bad idea for chicken but it doesn't sound like the way you like your steaks.

That being said, I have to call attention to a great idea Steven mentions in How To Grill p. 127. (How To Brine and Grill Pork Chops) In this recipe, the pork chops are first smoked in the grill for about 20 minutes before being moved directly over the heat. If you are smoking with a low temperature and your starting with a cool or even a cold steak or chop, this is a great way to get some extra smokey flavor and still keep all the advantages of cooking over high uncovered heat.